⇦Chinese Physics Letters, 2019, Vol. 36, No. 4, Article code 046101 Synthesis and Characteristics of Type Ib Diamond Doped with NiS as an Additive * Jian-Kang Wang (王健康)1,2,3, Shang-Sheng Li (李尚升)1,2,3**, Ning Wang (王宁)1, Hui-Jie Liu (刘慧杰)1, Tai-Chao Su (宿太超)1,2,3, Mei-Hua Hu (胡美华)1,2, Fei Han (韩飞)1,2,3, Kun-Peng Yu (于昆鹏)1,2,3, Hong-An Ma (马红安)4 Affiliations 1School of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454000 2Engineering Technology Research Center of Jiaozuo City for Advanced Functional Materials Preparation under High Pressure, Jiaozuo 454000 3Henan Joint International Research Laboratory for High Performance Metallic Material and Their Numerical Simulation, Jiaozuo 454000 4State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012 Received 23 January 2019, online 23 March 2019 *Supported by the National Natural Science Foundation of China under Grant No 51772120, the Natural Science Foundation of Henan Province under Grant No 182300410279, the Project for Key Science and Technology Research of Henan Province under Grant No 182102210311, the Program for Innovative Research Team in Science and Technology in the University of Henan Province under Grant No 19IRTSTHN027, and the Professional Practice Demonstration Base for Professional Degree Graduate in Material Engineering of Henan Polytechnic University under Grant No 2016YJD03.
**Corresponding author. Email: lishsh@hpu.edu.cn Citation Text: Wang J K, Li S S, Wang N, Liu H J and Su T C et al 2019 Chin. Phys. Lett. 36 046101    Abstract Large diamond single crystals doped with NiS are synthesized under high pressure and high temperature. It is found that the effects on the surface and shape of the synthesized diamond crystals are gradually enhanced by increasing the NiS additive amount. It is noted that the synthesis temperature is necessarily raised to 1280$^{\circ}\!$C to realize the diamond growth when the additive amount reaches 3.5% in the synthesis system. The results of Fourier transform infrared spectroscopy (FTIR) demonstrate that S is incorporated into the diamond lattice and exists in the form of C–S bond. Based on the FTIR results, it is found that N concentration in diamond is significantly increased, which are ascribed to the NiS additive. The analysis of x-ray photoelectron spectroscopy shows that S is present in states of C–S, S–O and C–S–O bonds. The relative concentration of S compared to C continuously increases in the synthesized diamonds as the amount of additive NiS increases. Additionally, the electrical properties can be used to characterize the obtained diamond crystals and the results show that diamonds doped with NiS crystals behave as n-type semiconductors. DOI:10.1088/0256-307X/36/4/046101 PACS:61.72.S-, 61.72.U-, 81.10.-h © 2019 Chinese Physics Society Article Text Diamond's structure is a face-centered cubic Bravais lattice. The structure consists of two face-centered cubic lattices nested by 1/4 units offset along the volume diagonal of the cubic cell. In the midpoint of the four diagonal lines that are not adjacent to each other, one atom is added to obtain a diamond lattice structure. The space group is $Fd\bar{3}m$ (No. 227). Each C atom has four nearest neighboring atoms and forms the C–C covalent bond with the four adjacent atoms in the form of $sp^3$ hybrid orbits. The stable structure with a covalent bond gives diamond its hardness and high melting point. Therefore, diamond is widely used in various fields.[1-4] At the same time, more excellent properties of diamonds are constantly explored. For example, in terms of electrics, the insulator properties of diamond could be converted to semiconductor properties by doping a suitable donor or acceptor element.[5-8] In terms of its optical properties, the transformation of nitrogen centers in the type-Ib diamond after annealing treatment affect the color of the diamond.[9] In addition, the color center in the diamond could be used in quantum information science.[10-12] First-principles calculations indicate that S could act as the donor impurity to improve the electrical conductivity of diamond.[8] Furthermore, a diamond film doped with S has been prepared by chemical vapor deposition (CVD), which exhibits n-type semiconductor characteristics.[13,14] Sato and Palyanov used sulfur element as a non-metallic catalyst to synthesize type-Ib diamonds under high pressure and high temperature (HPHT) conditions. However, the synthesized diamond had a poor crystal shape and small size.[15,16] Zhang et al. successfully synthesized single crystal diamonds co-doped with B and S, which showed p- or n-semiconductor properties. They also studied the effects of the additives on synthesis and morphology of diamonds.[7,17] However, there is a lack of the assessment of impurity concentrations in the obtained diamond. In contrast, Chen et al. synthesized type-IIa diamond doped with S and S located at the diamond lattice in the form of C–S and C–S–O bonds. However, the amount of the incorporated S into the diamond was very small.[18] In our previous study, we[19] successfully synthesized diamond doped with FeS additive, using the (111) plane as a growth surface. We also analyzed and evaluated the existence, form and effective amount of S in the synthetic diamond. By comparing the concentration of S in large single crystal diamond doped with elementary S, high concentration S in diamond was synthesized using compound FeS as an additive. However, the inclusions in diamond were more obvious when the amount of additive FeS was small and high quality S-doped diamond could not be synthesized. Therefore, NiS is used as a dopant to synthesize large single crystal diamond in the FeNi-C system. Therefore, the synthesis conditions of high quality diamond with the sheet-like morphology and the effect of NiS doping on diamond are investigated in this paper. The synthesis equipment to produce diamond by the temperature gradient method (TGM) is a home bred cubic anvil HPHT apparatus (SPD6$\times 1200$). The diamond synthesis pressure is about 5.6 GPa and the synthesis temperature is about 1250$^{\circ}\!$C–$1280^{\circ}\!$C. Flake FeNi catalyst (the weight ratio of Fe:Ni is 64:36) and high purity graphite powder (purity$>$99.9%) are selected as the experimental materials. NiS powders (with 99.9% purity) are employed as the dopant to providing S resource. The particle size of the seed crystal is about 0.8 mm and the (100) plane is selected as the growth surface. The color, crystal shape and defect of diamonds after acid treatment are observed using an optical microscope (OM). The presence or absence of C, N and S in the diamond lattice is measured using infrared technology (Bruker Optics/IFSHyperion 3000M). Meanwhile, the state and relative concentration of S in diamond lattice are measured by x-ray photoelectron spectroscopy (XPS) (PHI X-tool). The concentration of S in diamond is evaluated by calculating the areas of S $2p$ peak relative to that of the C $1s$ peak. The electrical properties of diamond are measured using the four-point probe and Hall effects method. To investigate the effects of NiS additive on diamond growth, diamonds doped with NiS are synthesized under 5.6 GPa. As listed in Table 1, diamonds doped with different amounts of additive NiS are obtained at 1250$^{\circ}\!$C (samples a–d) or at 1280$^{\circ}\!$C (sample e). The corresponding optical photographs to the obtained samples are displayed in Fig. 1.
Table 1. Experimental results of lager diamonds doped with different amounts of additive NiS in the FeNi-C system.
Sample NiS (wt.%) Temperature ($^{\circ}\!$C) Growth time (h) Inclusions
a 0 1250 10 No
b 1 1250 10 No
c 1.5 1250 10 No
d 2.5 1250 10 A little
e 3.5 1280 10 A little
In the diamond growth V-shaped region, the crystal shape of diamond grown along the (100) plane translates from the plate shape to middle tower, even to the tower shape as the synthesis temperature increases.[20] It can be seen from Figs. 1(a)–1(d) that the crystal shapes of diamonds doped with different amounts of NiS have plate shapes. Additionally, the (111) planes at the four corners of samples a–c continuously decreases and the (100) plane continuously increases, with increasing the addition amount of NiS. When the addition amount of NiS is 1.5%, the four corners of sample c completely disappear and the area of (100) plane reaches the maximum. According to the bald point model,[21] C on the (100) plane is replaced by S and will combine more C than that on the (111) plane. However, the main driving force of diamond growth is temperature gradient at the axial in the growth cell. The diamond growth along the (100) plane is plate shaped at 1250$^{\circ}\!$C and 5.6 GPa. Moreover, the (111) plane of diamond is a double-layered dense surface, where the internal interaction between the two layers is strong but the interaction between the adjacent two layers is weak. During the diamond growth process, the crystal surface has a tendency to grow toward (111) plane. Both the temperature gradient and arrangement structure of C on different crystal planes determine that (111) plane of the diamond doped with a small amount of NiS preferentially disappears. Therefore, when the amount of additive NiS is small, the effect of NiS doped on the crystal shape of diamond is weak. When the addition amount of NiS is 2.5%, the front (100) plane of the diamond becomes significantly smaller and the crystal shape changes to a middle tower shape. This phenomenon can be explained by the bald point model. Diamond doped with amount of 3.5% NiS cannot be synthesized at 1250$^{\circ}\!$C. Therefore, the synthesis condition of diamond is adjusted and the tower shape diamond doped with amount of 3.5% NiS is synthesized at 1280$^{\circ}\!$C. Although diamond doped with NiS at larger dosages is successfully synthesized, its quality is relatively poor. We find that the effect of NiS doping on diamond growth is different from that of FeS doping on diamond.[19] By increasing the addition amount of FeS, the inclusions in the obtained diamond increase and crystal quality decreases under HPHT. However, synthesis of diamond is unaffected when the amount of FeS is increased. In contrast, the V-shaped region of S-doped diamond moves to the lower left[6] with increasing the amount of S content in the FeNiMnCo-C system. However, when the amount of additive NiS reaches a certain level (at 3.5%), the diamond cannot be nucleated and grow at 1250$^{\circ}\!$C. Compared to the color of diamond doped with NiS, type-Ib diamond is dim (Fig. 1(a)). However, diamond crystals doped with NiS are brighter, as shown in Figs. 1(b) and 1(c). As displayed in Fig. 1(d), the diamond becomes black when the NiS amount in the synthesis system is 2.5%. In addition, we find that color of four corners in diamond (Fig. 1(c)) is darker than that in diamond (Fig. 1(b)). This is due to the fact that the additive impurities preferentially enter into the diamond lattice from the (111) plane of diamond.[22,23] The diamond displays a complete crystal shape and a translucent color when the amount of NiS added is 1.5%, which indicates a high quality diamond. However, the visible inclusions in the diamond obviously increase with a further increase of the addition amount of additive NiS in the synthesis system, which results in a decrease in the diamond's quality.
cpl-36-4-046101-fig1.png
Fig. 1. Photograph of large diamonds synthesized with different amounts of additive NiS: (a) 0%, (b) 1%, (c) 1.5%, (d) 2.5%, and (e) 3.5%.
To investigate whether or not S has been successfully incorporated into the diamond, the diamonds that we obtained are characterized using FTIR.[24] The measurement results are shown in Fig. 2, curves a–e correspond to diamonds synthesized in Fig. 1, respectively. The characteristic peaks of N locate at 1130 cm$^{-1}$ and 1344 cm$^{-1}$ in the ideal type-Ib diamond.[25] The spectra shown in Figs. 2(a) and 2(b) have characteristic peaks of N, while the spectra in Figs. 2(d) and 2(e) do not have characteristic peaks of 1130 cm$^{-1}$ due to the poor quality of the crystals. Furthermore, both curves b and c have characteristic peaks of C–S bonds with a wave number of 871 cm$^{-1}$.[26] This indicates that S is successfully incorporated into the diamond lattice in the form of C–S bond. By comparing the absorption intensity of N-peak in Fig. 2(a), we find that the absorption intensity of that in Figs. 2(b) and 2(c) is prominent. Therefore, according to the formula[25,27] $$\begin{align} C_{\rm N} =(25\pm 2)\times \alpha (1130\,{\rm cm}^{-1}),~~ \tag {1} \end{align} $$ where $C_{\rm N}$ represents N concentration, and $\alpha $ (1130 cm$^{-1}$) represents the value corresponding to peak 1130 cm$^{-1}$, we calculate N concentration ($C_{\rm N}$) in the diamonds and the results are listed in Table 2. It can be seen from Table 2 that $C_{\rm N}$ in the diamond without NiS additive is 95 ppm. However, the N concentrations of the diamond doped with 1% and 1.5% NiS are 392 ppm and 312 ppm, respectively. Due to the poor quality of diamond crystals (Figs. 1(d) and 1(e)), the corresponding characteristic peak of N is not obvious (Fig. 2(d)), and its nitrogen concentration is not calculated. On the one hand, Isaac and Lawson[28] pointed out that Ni as a catalyst could facilitate the increase of N concentration of the synthesized diamond. On the other hand, the N-peak of diamond doped with FeS is not significant in the infrared spectrum and $C_{\rm N}$ is small in diamond.[19] Therefore, it is indicated that NiS as a dopant has an important influence on the increase of $C_{\rm N}$ in the synthesized diamond.
cpl-36-4-046101-fig2.png
Fig. 2. The FTIR absorption spectra of diamonds with different amounts of additive NiS: (a) 0%, (b) 1%, (c) 1.5%, (d) 2.5%, and (e) 3.5%.
Table 2. The values of $C_{\rm N}$ in diamonds doped with different amounts of NiS.
Sample a b c d e
NiS (%) 0 1 1.5 2.5 3.5
C$_{\rm N}$ (ppm) 95 392 312
To evaluate effective the doping amount of S in diamond, diamonds doped with NiS are measured by XPS. Consequently, the spectra of C $1s$ and S $2p$ in diamond are obtained. The measurement results of diamond with 1.5% NiS are shown in Figs. 3(a) and 3(b). In addition, the areas of S $2p$ peak relative to that of C $1s$ peak in diamond is calculated. The calculation results of diamonds with different amounts of additive NiS are listed in Table 3.
cpl-36-4-046101-fig3.png
Fig. 3. XPS spectra of diamond with NiS doped at 1.5%: (a) C$1s$ and (b) S $2p$.
Figure 3(a) gives the C $1s$ spectra of diamond doped with amount of 1.5% NiS. The de-convolution of C $1s$ spectra gives two signal peaks at 284.3 and 284.8 eV. Figure 3(b) is S $2p$ spectra of diamond doped with the amount of 1.5% NiS. The spectra of S $2p$ can be resolved into three signals with binding energies of 168.4 eV, 168.6 eV and 169.1 eV. According to NIST XPS database and literature,[19,29-32] the de-convolution peak at 284.3 eV can be contributed from the C–C bond and the peak at 284.8 eV is due to the C–S–O bond. The C–S–O bond contributes a signal peak of 168.4 eV, the S–O bond contributes a signal peak of 168.6 eV, and C–S contributes a signal peak of 169.1 eV. Furthermore, the C $1s$ and S $2p$ spectra of diamond doped with FeS has the same signal peak as those of diamond doped with NiS.[19] It can be seen that S is incorporated into the diamond and exists in diamond in the forms of C–S, S–O and C–S–O bonds. Meanwhile, S exists in the same state of bond in diamond with sulfide (FeS/NiS) as a dopant. The relative concentrations of S relative to C ($C_{\rm S}$) in diamond with different amounts of additive NiS are listed in Table 3. It is clearly seen from Table 3 that the $C_{\rm S}$ values are 4.63%, 9.89%, 14.86% and 17.56%, corresponding to amounts of doping NiS of 1%, 1.5%, 2.5% and 3.5%, respectively. This shows that $C_{\rm S}$ is continuously increasing in diamond with the addition amount of additive NiS. When $C_{\rm S}$ is 14.86% (Table 3, sample d), the color of the obtained diamond (Fig. 1(d)) changes significantly. The results by XPS spectra are consistent with the results by the FTIR analysis. However, the qualities of the diamond crystals are poorer (Figs. 2(d) and 2(e)) when $C_{\rm S}$ is larger (Table 3, samples d and e).
Table 3. The concentrations of S relative to C in diamond with NiS doped.
Sample NiS (wt.%) $C_{\rm S}$ (%)
b 1 4.63
c 1.5 9.89
d 2.5 14.86
e 3.5 17.56
Both XPS and FTIR tests indicate that S is incorporated into the diamond. To study the electrical properties of the synthesized diamond crystals, the electrical performance tests of diamonds with NiS doping are run using a four-point probe and Hall effects method.[7] The Hall coefficient, resistivity, Hall mobility and carrier density of doping diamond are obtained by $$\begin{align} \mu_{\rm H} =\,&R_{\rm H}/\rho,~~ \tag {2} \end{align} $$ $$\begin{align} n=\,&r_{\rm H}/(R_{\rm H} e),~~ \tag {3} \end{align} $$ where $\mu_{\rm H}$ is the Hall mobility, $\rho$ is the resistivity, $R_{\rm H}$ is the Hall coefficient, $n$ is the carrier density, and $r_{\rm H}$ is the Hall factor ($r_{\rm H}$ generally takes 1). The results are listed in Table 4.
Table 4. The measurement results of the electrical properties of diamonds with NiS doped.
Sample NiS (wt.%) $R_{\rm H}$ (cm$^{3}$/C) $\rho$ ($\Omega\cdot$cm) $\mu_{\rm H}$ (cm$^{2}$/Vs) $n$ (cm$^{-3}$)
a 0 $3.543\times 10^{17}$ $2.239\times 10^{10}$ $1.583\times 10^{7}$ 2
b 1 $-1.156\times 10^{9}$ $4.832\times 10^{6}$ 239.238 $5.400\times 10^{9}$
c 1.5 $-0.751\times 10^{9}$ $3.213\times 10^{6}$ 233.738 $8.312\times 10^{9}$
d 2.5 $-0.706\times 10^{9}$ $1.163\times 10^{6}$ 607.051 $8.842\times 10^{9}$
e 3.5 $-1.951\times 10^{9}$ $12.328\times 10^{6}$ 158.258 $3.199\times 10^{9}$
The electrical properties of diamond are listed in Table 4, corresponding to the crystals in Fig. 1. It can be seen from the results that Hall coefficients of diamond doped with NiS in Table 4 is negative, therefore they are an n-type semiconductor. We also find that the resistivity of NiS doping diamond (a–d in Table 4) continuously decreases as the additive amounts are increased. This result is in line with the effect of elementary S doping on diamond.[7] The resistivity of sample e is larger than that of other doping samples due to the poor quality of crystal in Fig. 1(e). The resistivity of S doping diamond with 3% dosage is $1.312\times 10^{6}$ $\Omega \cdot$cm,[7] while the resistivity of diamond doping with NiS (2.5% dosage) is $1.163\times 10^{6}$ $\Omega$$\cdot$cm. Additionally, Hall mobility and carrier density of diamond gradually enhance with increasing amounts of additive NiS, reaching a maximum of 607.051 cm$^{2}$/Vs and $8.842\times 10^{9}$ cm$^{-3}$, respectively. In contrast, the S doping nano-crystalline diamond film has low carrier mobility and high charge density.[33] Therefore, diamond doped with NiS as an n-type semiconductor has better potential applications in electronics. In summary, large diamond single crystals doped with NiS have been synthesized under 5.6 GPa and 1250$^{\circ}\!$C–$1280^{\circ}\!$C. The (111) plane at the four corners of diamond is continuously shrunk and the front (100) plane is continuously enlarged as the amount of NiS in the synthesis system is increased. The FTIR result indicates that S exists in the obtained diamond crystals in the form of C–S bond. The value of $C_{\rm N}$ in the synthesized diamond crystals increases, due to the addition of NiS additive. In addition, XPS measurement results show that S exists in the forms of C–S, S–O and C–S–O bonds in the synthesized diamond. Furthermore, $C_{\rm S}$ in the diamond samples is enhanced as the amount of additive NiS is increased. In addition, the electrical measurement shows that high quality diamond crystals doped with NiS behave as an n-type semiconductor, which lays the foundation for the further exploration of S-doped diamonds. References Development of a micro diamond grinding tool by compound processAn experimental study on a novel diamond whisker wheelDiamond growth rates and physical properties of laboratory-made diamondBoron-Doped Diamond-Film-Based Two-Dimensional Electrode of Electrophoresis TankStudy on synthesis and electrical properties of slab shape diamond crystals in FeNiMnCo-C-P system under HPHTn-type conductivity of phosphorus-doped homoepitaxial single crystal diamond on (001) substrateLarge single crystal diamond grown in FeNiMnCo–S–C system under high pressure and high temperature conditionsN-type B-S co-doping and S doping in diamond from first principlesCharacterization of Various Centers in Synthetic Type Ib Diamond under HPHT AnnealingQuantum nanophotonics in diamond [Invited]Si-doped nano- and microcrystalline diamond films with controlled bright photoluminescence of silicon-vacancy color centersGrowth and Characterization of the Laterally Enlarged Single Crystal Diamond Grown by Microwave Plasma Chemical Vapor Depositionn-Type Control by Sulfur Ion Implantation in Homoepitaxial Diamond Films Grown by Chemical Vapor DepositionSulfur: A donor dopant for n -type diamond semiconductorsHigh-pressure synthesis and characterization of diamond from a sulfur–carbon systemSulfur: a new solvent-catalyst for diamond synthesis under high-pressure and high-temperature conditionsEffect of B-S co-doping on large diamonds synthesis under high pressure and high temperatureSynthesis and characterization of IIa-type S-doped diamond in FeNi catalyst under high pressure and high temperature conditionsEffect of FeS doping on large diamond synthesis in FeNi–C systemEffects of the additive boron on diamond crystals synthesized in the system of Fe-based alloy and carbon at HPHTEffect of additive boron on type-Ib gem diamond single crystals synthesized under HPHTReaction Mechanism of Al and N in Diamond Growth from a FeNiCo-C SystemEffects of the additive NaN3 added in powder catalysts on the morphology and inclusions of diamonds synthesized under HPHTDetermination of the energies of combustion and enthalpies of formation of nitrobenzenesulfonamides by rotating-bomb combustion calorimetryThe nitrogen content of type Ib synthetic diamondThe effect of nickel and cobalt on the aggregation of nitrogen in diamondInfluence of doping on the electron spectrum of siliconA surface analytical and an electrochemical study of iron surfaces modified by thiolsXPS core level spectra and Auger parameters for some silver compoundsStructural and Electrical Properties of Sulfur-Doped Diamond Thin Films
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